2. According to the national standard, the selection principle of protective tube as protective cable is: the inner diameter of the tube is not less than 65438+ 0.5 times of the outer diameter of the cable, and it should be increased when there are more than two bends. The outer diameter of WDZ-YJFE4x25+1X16 cable is 26.2mm, and the allowable value in the specification is that the pipe diameter is 40% larger than the wire diameter.